On motor vehicles, the illuminating means increasingly takes the form of LEDs. With these lamps, there is the problem that owing to the possible high operating voltages of the network aboard, which usually lie between 9 and 16 volts, the lamps generate great power losses at high voltages. If the lamps are designed for full brightness at the typical rated operating voltage of 13.5 V, distinctly higher power outputs result when such lamps are employed in a 16 V on-board network, since the bias resistance design boosts the current more than proportionally. The components present in the lamp, such as LEDs, resistors, elements of synthetic material and the like, thus reach their load limits, since the temperature in the lamp and on the conductor plates increases sharply owing to the more than proportional current increase. At today's packing densities of the LEDs in the lamps, safeties must be built into the lamp design for this reason. This leads to a high technical outlay. To keep it reasonably low, the brightness of the lamps is not fully utilized at rated voltage on this account. Also, cooling devices are provided, but this again leads to an additional design outlay.
Another problem consists in that present-day motor vehicle on-board networks always become unstable. This is attributable to the increasing number of auxiliary electrical systems with great current demand in the motor vehicle. Examples of such auxiliary electrical systems are electric steering, window raisers, accessory heating and the like. These systems are liable to frequent voltage breakdowns, especially in the case of fast-responding LED lamps specifically. These voltage breakdowns manifest themselves in clearly visible brightness fluctuations.